JP2009202224A - Evaluation method of partial penetration welding in fatigue resistance steel - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technique of quantitatively evaluating improved quantity of fatigue strength in the case of applying fatigue resistance steel to a steel deck plate structure. <P>SOLUTION: In a method of evaluating partial penetration welding in fatigue resistance steel; near a weld zone A in a steel deck plate structure to which fatigue resistance steel is applied, there is arranged in abutment a focusing type oblique angle probe 7 that can emit an ultrasonic flaw inspection beam at a prescribed oblique angle from the abutting face. By measuring an echo height on the incident angle line of the inspection beam of the probe, and thereby referring to a calculation curve prepared in advance using a notch specimen, the penetration prediction amount of the weld zone is determined. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a technique for evaluating the welding quality of partial penetration welding of a welded structure using fatigue resistant steel by ultrasonic flaw detection.

In a welded structure, fatigue cracks may occur starting from the welded part due to long-term service. Even in bridges as welded structures, fatigue damage, which is thought to be due to a significant increase in traffic volume and the effect of overloaded vehicles, has been observed.
In the steel slab structure, examples of fatigue damage such as joints between the deck plate and U-ribs have been reported. In particular, fatigue cracks that penetrate the plate thickness of the deck plate starting from the weld root are detected as cracks. This is an important issue for road maintenance.
In particular, fatigue cracks that occur at the root of the joint are cracks that may be affected by road traffic such as road depression, despite the difficulty of finding cracks due to pavement on the deck plate. Because there are, the importance is very large.

JP-A-7-242992 (see Patent Document 1) discloses fatigue resistant steel. Fatigue-resistant steel is a dual-phase steel in which ferrite (soft phase) and bainite (hard phase) are optimally arranged. While maintaining strength, toughness, weldability, and workability at or above those of conventional steel, welding is performed. This is a steel material with improved fatigue crack initiation characteristics and fatigue crack growth resistance of the base metal.
Preferred examples of the structure of the fatigue resistant steel are, in mass%, C: 0.01 to 0.3%, Si: 0.1 to 0.5%, Mn: 0.3 to 2.0% and sol. Al: 0.005 to 0.1%, and Cr: 1.5 % Or less (optional) Mo: 0.6% or less (optional) Ni: 0.5% or less (optional) Cu: 1.0% or less (optional) Nb: 0.1% or less (It may be additive-free), Ti: 0.1% or less (may be additive-free) and V: 0.1% or less (may be additive-free), the balance is a steel plate made of Fe and inevitable impurities, and its structure is hard There is a steel plate having a fatigue crack growth inhibiting effect characterized in that the hardness difference between the two parts is 150 or more in terms of Vickers hardness.
Or, in mass%, C: 0.01 to 0.3%, Si: 0.1 to 0.5%, Mn: 0.3 to 2.0% and sol.Al: 0.005 to 0.1%, and Cr: 1.5% or less (may be added) Mo: 0.6% or less (may be additive-free), Ni: 0.5% or less (may be additive-free), Cu: 1.0% or less (may be additive-free), Nb: 0.1% or less (may be additive-free), Ti: 0.1% or less (may be additive-free) and V: 0.1% or less (may be additive-free), the balance being a steel plate made of Fe and inevitable impurities, the structure of which was dispersed in the base of the hard part and this base A steel sheet having a fatigue crack growth-inhibiting effect, comprising a soft part, wherein the hardness difference between the base of the hard part and the soft part is 150 Vickers hardness or more and the average particle size of the soft part is 50 μm or less. .
Or, in mass%, C: 0.01 to 0.3%, Si: 0.1 to 0.5%, Mn: 0.3 to 2.0% and sol.Al: 0.005 to 0.1%, and Cr: 1.5% or less (may be added) Mo: 0.6% or less (may be additive-free), Ni: 0.5% or less (may be additive-free), Cu: 1.0% or less (may be additive-free), Nb: 0.1% or less (may be additive-free), Ti: 0.1% or less (may be additive-free) and V: 0.1% or less (may be additive-free), the balance being a steel plate made of Fe and inevitable impurities, the structure of which consists of a hard part and a soft part. A steel sheet having a fatigue crack growth-inhibiting effect is characterized in that the hardness difference between the two parts is 150 or more in terms of Vickers hardness and the average interval between the hard parts is 50 μm or less.

Japanese Patent Laid-Open No. 7-242992

The object of the present invention is to quantitatively evaluate the improvement in fatigue strength when fatigue resistant steel is applied to a steel slab structure, and employs an ultrasonic flaw detection technique as its means.

In the evaluation method of partial penetration welding in fatigue-resistant steel according to the present invention,
In the vicinity of the welded part in the steel slab structure to which fatigue resistant steel is applied, a converging oblique probe that can irradiate an ultrasonic flaw detection beam at a predetermined oblique angle from the contact surface is placed in contact with it,
By measuring the echo height on the incident angle of the probe's flaw detection beam,
Referring to the calculation curve created in advance using the notched specimen,
Calculate the expected penetration of the weld.
Note that. The calculation curve can be created by the following procedure.
1) Create a stepped horizontal hole test piece by providing horizontal holes with different depths in the material made of fatigue resistant steel.
2) The height of the reflected echo from each side hole is measured, and the relationship between the depth of each side hole and the height of the reflected echo is plotted to obtain a distance amplitude characteristic curve.
3) The height of the reflected echo from the side hole of a specific depth is set as the reference sensitivity, and the relative reflected echo height of the distance amplitude characteristic curve with respect to this reference sensitivity is set as the relative echo height.
4) Create multiple notch specimens made of fatigue-resistant steel for each notch amount, and plot the curve obtained by plotting the relationship between each notch amount and the relative echo height of the notch specimen. Create as.

According to the evaluation method of partial penetration welding in fatigue-resistant steel according to the present invention,
Measure the echo height on the incident angle line of the flaw detection beam of the probe placed near the weld,
By referring to the calculation curve created in advance using the notched specimen,
It was possible to evaluate the partial penetration welding by calculating the expected penetration of the weld with high reliability.
When creating the calculation curve,
Using a stepped horizontal hole test piece made of the same material as the evaluation target material, obtain a distance amplitude characteristic curve, obtain a relative echo height relative to the reference sensitivity,
Since multiple notch test pieces are created for different notch amounts, and the curve obtained by plotting the relationship between each notch amount and the relative echo height in the notch test piece is created as a calculation curve,
It was possible to evaluate the partial penetration welding by calculating the expected penetration of the weld with high reliability.

Below, the evaluation method of the partial penetration welding in the fatigue-resistant steel concerning this invention is demonstrated in detail based on drawing which showed the embodiment.
In the evaluation method according to the present invention, first, a calculation curve for evaluation is created by the following procedure.
1) Create a stepped horizontal hole test piece by providing a horizontal hole with a different depth (3 mm to 12 mm) in a material of fatigue resistant steel of the same quality as the material to be evaluated. See FIG.
In FIG.
A φ2.0mm horizontal hole penetrating in the width direction at a position 3mm deep from the surface of the material 1 for a plate-shaped test piece 19mm thick and 25mm wide made of fatigue resistant steel of the same quality as the material to be evaluated 2 was provided. Similarly, horizontal holes 2 having a depth of 4.5 mm, 6.0 mm, 7.5 mm, 9.0 mm, 10.5 mm, and 12 mm were provided at intervals of 20 mm to obtain a test piece 3.
Then, a focusing type two transducer oblique angle probe is installed on the surface of the test piece 3 to experiment with the intensity change of the reflected vibration (echo height) when ultrasonic vibration is applied. A distance amplitude characteristic curve as shown was obtained. The characteristic of the intensity of the intermediate reflected vibration is M line, the characteristic of 6 dB stronger than this M line is H line, and the characteristic of 6 dB weak intensity is L line.
As the flaw detection angle of the converging type two transducer oblique angle probe, a 70 ° probe and a 75 ° probe were used.

(1) In FIG. 2, the horizontal axis indicates the beam path length (mm), and the vertical axis indicates the echo height (%).
(2) As a reference value, a reflected echo from a lateral hole (depth 5 mm) of RB-41-NO.1φ3 mm was used as a reference sensitivity, and this reference sensitivity was adjusted to the H line of the distance amplitude characteristic curve.

(3) A notch test piece 4 simulating partial penetration of U-rib welding as shown in FIG. 4 was made of fatigue-resistant steel.
The notch test piece 4 shown in FIG. 4 has a plate shape of 80 mm × 80 mm × 6.8 mm (thickness), and a notch 41 having a notch amount Sr and a width of 20 mm is formed along one side. Yes. The inclination angle of the boundary between the notch 41 and the non-notch 42 was 12.5 °.
In the schematic diagram at the time of welding shown in FIG.
A case is shown in which a fatigue-resistant steel having a thickness of 12 mm is used as a steel floor plate 5 and a U-rib 6 having a shape corresponding to the notch test piece shown in FIG. 4 is welded thereto.
In (b) of FIG. 3 which showed the schematic diagram after welding,
In the welded portion A, the U-rib 6 having a notch test piece-equivalent shape is in a state where the U-rib edge surface and the deck surface of the steel floor plate are in close contact with each other due to welding shrinkage during U-rib welding.
As shown in FIG. 3 (b), the focusing type dual transducer oblique probe 7 is installed on the surface of the U-rib 6 so that the ultrasonic beam direction faces the welded portion A, By varying the notch amount Sr in various ways and plotting the relationship between the notch amount Sr and the relative echo height Hds, the following FIGS. 5 and 6 were obtained.

(4) By measuring the ultrasonic flaw detection of the U-rib welded specimen 6 and the residual penetration amount Wr of the macro test piece and plotting the relationship between the residual penetration amount Wr and the relative echo height Hdw, FIG. 8 was obtained.

<Ultrasonic flaw detection results>
(1) Measurement result of notched specimen
Using two types of probes, 70 ° probe and 75 ° probe, ultrasonic testing was conducted on the notched specimen, and the notch amount Sr and relative echo height Hds as shown in Figs. A curve showing the relationship (hereinafter simply referred to as “calculation curve”) was obtained. FIG. 5 shows the calculation curve when the plate thickness is 6 mm, and FIG. 6 shows the calculation curve when the plate thickness is 8 mm. When the calculation curve a is a 70 ° probe, the calculation curve b is a 75 ° probe, and the curve c is a theoretical value.
According to these calculation curves a and b, the relationship between the notch amount Sr and the relative echo height Hds is inclined until the notch amount is about 1/3 of the plate thickness. Regardless of the notch amount Sr, the relative echo height Hds is a substantially constant value. Such a tendency almost coincided with the curve c based on the theoretical formula (JSNDI textbook “Ultrasonic Flaw Test II P82 to P84, supervised by the Nondestructive Inspection Association”) regarding the plane flaw orthogonal to the ultrasonic beam.

(2) Measurement results of U-rib welded specimen Next, using a 75 ° probe, the U-rib specimen was subjected to ultrasonic flaw detection, and the amount of residual melt Wr and the relative echo height Hdw of the macro specimen were measured. The relationship between the amount of residual melt Wr and the relative echo height Hdw was plotted to obtain curves d and e shown in FIGS. FIG. 7 shows the case where the thickness of the U rib is 6 mm, and FIG. 7 shows the case where the thickness of the U rib is 8 mm. The vertical line f is a line indicating 75% penetration.
According to the curve d, when the relative echo height Hdw in the case of the U-rib plate thickness of 6 mm is in the range of −4.0 to +6.0 dB, the residual penetration amount Wr is deeper than the calculated curve. Is on the safe side. When the relative echo height Hdw exceeds +6.0 dB, the relative echo height Hds becomes a constant value from the calculation curve, and it is difficult to estimate the amount of residual melting Wr.
According to the curve e, the same tendency is observed when the thickness of the U rib is 8 mm.

  From the above results, it is possible to assume with sufficient reliability that the amount of residual penetration Wr in the U-rib welded specimen can be assumed based on the value of the relative echo height Hdw by using the calculated curve. It was revealed.

  As described above, by using the calculation curve, it became clear that the amount of residual penetration Wr in the U-rib welded specimen can be assumed based on the value of the relative echo height Hdw. Below, the evaluation method of the partial penetration welding in the steel deck structure of the fatigue-resistant steel which is an actual evaluation object is demonstrated.

1) Welding of U-ribs is performed in the actual steel deck structure to be evaluated.
2) The focusing oblique probe is brought into contact with the U-rib of the weld, and the relative echo height is measured.
3) Based on the obtained relative echo height, the expected amount of penetration of the weld is calculated with reference to the calculation curve.
4) When the calculated expected penetration amount satisfies a predetermined criterion (75% or more of the plate thickness), the weld is evaluated as acceptable.

  As described above, by using the calculation curve, it was possible to confirm and evaluate a penetration amount of 75% or more of the U-rib plate thickness of 6 mm by using the ultrasonic flaw detection technique.

As the focusing type oblique angle probe used in the evaluation method of the present invention, a focusing type dual vibrator oblique angle probe of 70 to 75 degrees is suitable.

It is a figure which shows the step type horizontal hole test piece used for the evaluation method of the partial penetration welding in the fatigue-resistant steel concerning this invention. It is a distance amplitude characteristic curve obtained using the test side of FIG. It is a schematic diagram at the time of welding. It is a figure which shows the shape of a notch test piece. This is a calculated curve based on a notched specimen (plate thickness 6 mm). It is a calculation curve based on a notched specimen (plate thickness 8 mm). It is a measurement result of a U-rib weld specimen (plate thickness 6 mm). It is a measurement result of a U-rib weld specimen (plate thickness: 8 mm).

Claims (2)

In the vicinity of the welded part in the steel slab structure to which fatigue resistant steel is applied, a converging oblique probe that can irradiate an ultrasonic flaw detection beam at a predetermined oblique angle from the contact surface is placed in contact with it,
By measuring the echo height on the incident angle of the probe's flaw detection beam,
Referring to the calculation curve created in advance using the notched specimen,
A method for evaluating partial penetration welding in fatigue-resistant steel, characterized by calculating an expected amount of penetration of a weld. The evaluation method according to claim 1, wherein a calculation curve created by the following creation procedure is used.
1) Create a stepped horizontal hole test piece by providing horizontal holes with different depths in the material made of fatigue resistant steel.
2) The height of the reflected echo from each side hole is measured, and the relationship between the depth of each side hole and the height of the reflected echo is plotted to obtain a distance amplitude characteristic curve.
3) The height of the reflected echo from the side hole of a specific depth is set as the reference sensitivity, and the relative reflected echo height of the distance amplitude characteristic curve with respect to this reference sensitivity is set as the relative echo height.
4) Create multiple notch specimens made of fatigue-resistant steel for each notch amount, and plot the curve obtained by plotting the relationship between each notch amount and the relative echo height of the notch specimen. Create as.

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